I go through this cycle where I diligently try to keep all my receipts until I can't stand the sight of them piling up like kindling and I throw them away.
But I just figured out (this is the stuff I should have learned in college) that I can reimburse myself from my health savings account for eligible expenses all the way back to when I first opened the account, which is so far back I can't remember (it was sometime after I had to start buying my own health insurance as a freelancer, and mostly I chose HSA policies for the tax-deductible contributions).
I have some cash in my HSA that I'd like to pillage (it's mostly invested, but they require a minimum pool of cash to sit around, for instances like this, I suppose), so I started searching for my past health expenses, but the only receipts I have are the ones I have are in Expensify, which I only started using last year (but still all those Walgreens and Target purchases add up, especially with the CARES Act adding over-the-counter drugs to the HSA eligible expenses).
I was also relying on my bank and credit card accounts to maintain a record of my expenses online, but typically they only go back so far, and also I closed the Wells Fargo account I'd been using for twenty years (I wasn't expecting a gold watch, but it would have been nice if they'd said something about my being a long-time customer when I closed it, but nope).
One restriction: you can't claim expenses that were already included in itemized deductions, but most years I spend four months adding up all my deductions for tax time only to end up using the standard deduction. Fortunately, I did keep copies of my tax returns going back ten years!